Funding is requested for the purchase of a JEM (JEOL) 1200 EXII TEMSCAN Analytical electron microscope at a cost of $392,805. The current Electron Microscope at this institution is a basic 1974 model Philips EM301 that does not meet the present-day needs of the PHS Supported Research. The Principal Investigators of 12 PHS-funded grants require an electron microscope with 1) advanced imaging system including secondary electron image, back-scattered electron image and scanning-transmission bright or dark-field images, 2) Eucentric side entry goniometer stage, 3) X-ray microanalysis, and 4) complete cryo-transfer system. An evaluation of 3 different makes of electron microscopes (JEOL, Hitachi, and Philips) reveal that the JEM (JEOL) 1200 EXII electron microscope is the instrument of choice. The research projects included in the application show that the usage of the requested instrument by the PHS-supported investigators exceeds 75% of the total use. The acquisition of a new electron microscope is essential for the rapid progress of health related research. The project descriptions provided in the application demonstrate that the new scope is needed for basic and clinical research including the pathogenesis of influenza-, paramyxo- and Epstein Barr viruses, chemotherapy of childhood solid tumors, pneumocystis infection in AIDS patients, studies of megakaryocytopoiesis, control mechanisms in immunoglobulin production, mechanisms of DNA replication, virus-cytoskeleton interaction and role of ubiquitin in cellular events.